1. Field of the Invention
The present invention relates to a method for winding up a magnetic recording medium, which comprises winding up a continuous polymeric substrate for the magnetic recording medium on which a magnetic layer is formed by a vacuum deposition procedure on a wind-up roll, and particularly the method in which the ends of both sides of the continuous polymeric substrate are masked during the vacuum deposition procedure.
2. Description of the Prior Art
Magnetic tapes with thin magnetic films thereon have drawn much attention due to the recent need for high density recording. The techniques for producing such magnetic tapes by means of a vacuum deposition procedure are well-known. The techniques comprise vacuum-depositing magnetic material on a continuous substrate while the substrate is applied on a rotating main drum for cooling, and thereafter winding up the substrate, on which a thin film-like magnetic layer is formed, on a wind-up roll. The vacuum deposition and winding-up processes are carried out in a vacuum atmosphere. In the case where such a substrate is wound up on a wind-up roll in a vacuum atmosphere, the ends of both sides of each reel of substrate are aligned with those of the other reels of substrate on the wind-up roll, whereby a raw winding roll on which the substrate with its both side ends aligned is produced, due to the air penetration into the interface between the respective adjacent reels of substrate being eliminated in the vacuum atmosphere.
When the magnetic material is vacuum-deposited on the substrate while the substrate is applied on the main drum, masking processing is applied to the regions each extending from the end portion of each side of the substrate toward the surface of the main drum. Accordingly, the magnetic material is deposited only on the central area on the substrate excluding the areas on the end portions of both sides of the substrate (hereinafter referred to as the side areas) each having a width from approximately several millimeters to scores of millimeters. This results in the varying thickness of the substrate in which the central area is thicker than the aforementioned side areas by the thickness of the magnetic layer.
The substrate which typically has a length of 4000-5000 m is wound up on a wind-up roll. Therefore, the difference in thickness between the central area and the side areas accumulates on an entire wind-up roll because of the winding effect of the substrate. Especially, in the case of the aforementioned techniques in which the substrate is wound up on a wind-up roll in a vacuum atmosphere, the difference in thickness between the central area and the side areas of the outermost reel of substrate on the wind-up roll is determined by the value which is calculated by multiplying the thickness of the magnetic layer by the number of revolutions around the wind-up roll, because no air is entrapped between the respective adjacent reels of substrate. Also, in this case, because the side ends of each reel of substrate are aligned with those of the other reels of substrate and because the boundaries between the central area and each of the side areas on each reel of substrate are aligned with the boundaries on the other reels of substrate, clear steps are generated at the respective boundaries on the outermost reel of substrate on the wind-up roll. Therefore, as the diameter of winding increases, defects such as winding wrinkles tend to appear at the aforementioned boundaries.
In view of the above problems, the general object of the present invention is to provide a method for winding up a magnetic recording medium in which winding wrinkles are prevented from occurring even when a continuous polymeric substrate for the magnetic recording medium having non-deposited areas on the end portions of both sides of the substrate is wound up in a vacuum atmosphere.
The specific object of the present invention is to provide a method for winding up a magnetic recording medium in which during winding up a continuous polymeric substrate for the magnetic recording medium on a wind-up roll the substrate is fluctuated relatively slowly in a width direction by a fluctuation range of at least 0.2 mm but at most 40 mm in a fluctuation cycle of at least 10 seconds but at most 1000 seconds thereby gradually shifting the position of each reel of substrate relative to the respective adjacent reels of substrate in a width direction, to prevent substantial steps from appearing at the boundaries between the central area and each of the side areas where the magnetic layer is not provided, and to eliminate the generation of winding wrinkles.